Aluminum Alloys for Packaging Applications

Extracto:

The first packaging use of aluminum, closures on glass bottles, dates to the early 1900’s. This was a successful application primarily because the closure could be made to hold tightly to the somewhat irregular glass threads. Aluminum foil was adopted for packaging shortly after its initial production in 1913.
Candy-bar and chewing gum wraps took advantage of many of the desirable properties of aluminum foil. Impact-extruded collapsible tubes of aluminum were introduced in the United States in 1921. In the late 1950’s, there was a trend toward adoption of aluminum for a broad range of rigid containers. The fabricating characteristics of aluminum permitted production of such containers by impacting, drawing, and adhesive bonding, as well as by spiral winding of foil laminates.

The first packaging use of aluminum, closures on glass bottles, dates to the early
1900’s. This was a successful application primarily because the closure could
be made to hold tightly to the somewhat irregular glass threads. Aluminum foil was adopted
for packaging shortly after its initial production in 1913.

Candy-bar and chewing gum wraps took advantage of many of the desirable properties of
aluminum foil. Impact-extruded collapsible tubes of aluminum were introduced in the
United States in 1921. In the late 1950’s, there was a trend toward adoption of aluminum
for a broad range of rigid containers. The fabricating characteristics of aluminum
permitted production of such containers by impacting, drawing, and adhesive bonding,
as well as by spiral winding of foil laminates.

Aluminum for packaging is preponderantly in the form of sheet or foil. Commercially pure
aluminum is mainly employed, although non-heat-treatable alloys of the aluminum-magnesium
and aluminum-manganese types are also used for higher strength. With both commercial-purity
aluminum and alloys, broad ranges in mechanical properties are available through varying
degrees of work hardening.

The uses of aluminum in packaging are identified by the industry in four categories:

Flexible wraps and laminates, incorporating foil

Rigid containers, made from sheet, foil laminates, or drawn heavy-gage foil, or
impact-extruded from slugs

Closures for bottles and jars, made from sheet or foil

Collapsible tubes, fabricated from slugs by impact extrusion.

Flexible Packaging

In the glossary of packaging terms, flexible packaging is defined as involving the use of
flexible materials such as foil, films, paper, and sheet, to form the container. Aluminum
foil has become firmly established as one of the major flexible packaging materials. About
85% of all aluminum foil produced is used in some form of packaging. The three major
packaging applications are household foil, 35%; laminated foil, 30%; and formed containers,
28.5%.

Aluminum foil is sheet less than 0.0060 in. (0.15 mm) thick. It can be rolled commercially
as thin as about 0.00017 in. (0.005 mm). An important characteristic of aluminum foil is
its high covering area per unit of weight.

Aluminum foil is outstanding in its low permeability to water vapor and gases. Extremely
small pinholes are unavoidable in thickness less than 0.001 in. (0.025 mm). Foil is
tasteless, odorless, nontoxic, and hygienic. A special advantage of annealed foil is that
it is substantially sterile because of the temperature (over 340°C or 650°F) of
annealing. Foil is greaseproof and nonabsorptive to liquids, and hence is especially suited
for packaging medicinal oils, ointments, grease-base cosmetics, and similar products. Foil
remains dimensionally stable during exposure to oils and greases.

Foil is an effective barrier to light and is used extensively to package photographic
materials and other light-sensitive products. Ultraviolet radiation accelerates the
development of rancidity in certain foods; foil is a good barrier to this radiation,
retarding loss in flavor and appearance, and inhibiting development of rancidity and
staleness.

Because it is an efficient reflector and low emitter of radiant heat, aluminum foil is
employed for packaging where the thermal insulating properties imparted by these
characteristics are advantageous. Despite these insulating effects, the good thermal
conductivity makes it possible to chill or heat aluminum packages more rapidly than those
with nonmetallic covering.

Alloys used for foil in packaging applications include 1100 (99.0 to 99.3 Al),
1145 (99.45 to 99.60 Al), 3003 (Al-1.25 Mn), and 5052
(Al-2.5 Mg-0.25 Cr). Annealed or soft foil is identified as O-temper. Annealing is
accomplished by heating the metal to above 340°C (650°F). This softens the foil,
removes traces of lubricants left from rolling, and effectively sterilizes it.

For many years, all the aluminum foil marketed commercially was in either the annealed or
the full-hard H19 temper. Foil gages above 0.002 in. (0.05 mm) are also available in the
intermediate, partially annealed tempers H25 and H27. Lighter gages in intermediate tempers
are available from a few foil sources. The hardest temper of foil, available in any gage
and designated H19, is an extra-hard temper that has received a high degree of cold
work.

Laminating, Coating, and Printing Materials. Unsupported foil in the light
gages used for packaging often lacks the ruggedness to withstand abuse encountered during
shipping and handling. For this reason, foil gages less than 0.001 in. (0.025 mm) are
generally laminated to paper or plastic films. In many instances, the foil also is coated
for protection, decoration, or heat sealing; usually, the laminate is printed for product
identification and appeal.

Heat sealing unites two or more surfaces by fusion, either of the base materials or of
coatings that have been applied, using controlled temperature, pressure, and dwell time.
The bond between the heat-sealed surfaces may be one of complete fusion or may be
partially fused to allow easy separation of the two surfaces. Laminated structures with
various types and weights of paper or plastic film perform satisfactorily under a wide
variety of conditions.

Coatings used on aluminum foil for protection can be formulated for resistance to
chemicals, heat, or scuffing. Resistance to chemical attack or to mechanical abuse can be
provided either by protective coatings or by various plastic films. In many applications,
a protective coating serves also as a heat-seal surface, as discussed subsequently.

Printing on aluminum foil can be accomplished by any commercial process, including
rotogravure, flexography, lithography, and letterpress. The foil generally is coated with
a washcoat or a primer prior to printing. Shellac washcoats normally are used for gravure
or flexographic printing, which utilize rapid-drying organic-solvent-base inks.

Rigid Containers

Rigid containers are stiff packages, usually of metal sheet and usually round in shape.
This type, known familiarly as "cans", originated in the days of Napoleon.
Some rigid containers employ foil laminated to a stiff nonmetallic backing sheet. Others
are smooth-wall containers drawn from heavy-gage foil. Rigid containers should protect
the product and withstand reasonable handling without deformation or breakage.

The can industry is the largest segment of the packaging complex. Cans are generally made
from steel, tin-coated steel, aluminum, a combination of fiber and aluminum foil, or
plastic. Most rigid containers are cylindrical. This shape utilizes the container material
efficiently, but the greatest advantage is that it permits manufacturing, drilling, and
closing at high speeds with exacting control. Almost all beer, beverage, vegetable, fruit,
dog food, and motor-oil containers are cylindrical.

Aluminum Alloys and Tempers. The aluminum alloys commonly used are 1100,
3003, 5052, 5082, 5086, and 5154. The tempers employed vary from the annealed condition,
used for impact can slugs, to the strain-hardened, extra-hard H19 temper for beer and oil
can ends. Intermediate work-hardened tempers are used where appreciable forming is
required. Gages range from 0.003 in. to 0.018 in. (0.075 to 0.45 mm), except for impact
or drawn-and-ironed bodies, which start as slugs or disks up to 0.125 in. (3 mm) thick.

The alloys with low yield strength and high elongation are easy to form, whereas those
with high yield strength and low elongation can be used only for simple forms such as
can ends.

Closures

A glass container consists of a glass body and a closure. Many years ago the closures were
cork, or a glass stopper, usually with a rubber-type gasket. Today, closures are made from
aluminum, tin plate, steel, plastic, or, sometimes, paper. Ideally, a closure must be
hermetically scalable, easily applied, and readily removable and recloseable. Attractive
appearance is advantageous for sales appeal. The cost should be low, but more important
in many applications is the need to protect the product. Furthermore, it is often desirable
to make the closure tamperproof.

Alloys and Characteristics. For many years, aluminum closures were
manufactured principally from 1100 alloy. During the 1920’s, alloys 3003 and 3004
were adopted, to take advantage of their higher mechanical properties with satisfactory
adhesion for the coatings then used. The H14 and H34 tempers have been used most
frequently.

About 1950, the aluminum-magnesium alloys, such as 5050 and 5052 in H36 temper, were
introduced for the larger-diameter closures, where higher strength is required. Stronger
alloys in full-hard or extra-hard tempers allow a reduction in metal gage. Gages commonly
used for closures are in the range of 0.006 to 0.012 in. (0.15 to 0.3 mm) for 3003 alloy
and somewhat thinner for 5052. For example, a closure normally made in 0.0095-in.
(0.25 mm) gage of 3003 may be satisfactory at 0.0085 in. (0.22 mm) with 5052-H19,
providing a reduction in gage of 10% and almost as much in cost. Advances in drawing
techniques are expected to promote greater use of the stronger tempers of 5052, including
the extra-hard H19.

Types and Applications. The rolled-on closure is the most popular,
and probably the most responsible for the extensive use of aluminum in closures. Many
variations of closures employ the rolled-on principle.

In addition to the various rolled-on designs, aluminum closures are made as screw cap,
hidden-thread screw cap, and tumbler cap.

Collapsible Tubes

A collapsible tube is defined as a cylinder of pliable metal that can be sealed in such
a manner that its contents, although readily discharged in any desired quantity, are
protected from contact with air or moisture. Products so packaged must flow under pressure
low enough not to damage the tube, but must be sufficiently viscous not to spill out of
the tube. Commercial production of aluminum collapsible tubes by impact extrusion began
in Switzerland in 1914 and in the United States in 1921.

After extrusion, the tubes are annealed to remove the work hardening and provide the
softness or limpness needed for good collapsibility. The degree of hardness that remains
in the annealed condition is needed for the tube to maintain its shape and to hold the
crimped fold at the closed end.

Coatings are required inside some aluminum collapsible tubes to prevent corrosion by
certain products. Even a superficial amount of corrosion, which might be tolerated
for other applications, is objectionable in the tubes, because gas produced by the
corrosion reaction causes the tube to swell. Consequently, coatings that provide a high
degree of protection against corrosion are required.

Buscar en la base del conocimiento

The Total Materia database contains many thousands of aluminum materials across a large range of countries and standards.

Where available, full property information can be viewed for materials including chemical composition, mechanical properties, physical properties, advanced property data and much more.

Using the Advanced Search page, define the search criteria by selecting ‘Aluminum’ in the Group of Materials pop-up list. It maybe that you need to further narrow the search criteria by using the other fields in the Advanced Search page e.g. Country/Standard.

Then click Submit

A list of materials will then be generated for you to choose from.

After clicking a material from the resulting list, a list of subgroups derived from standard specifications appears.

From here it is possible to view specific property data for the selected material and also to view similar and equivalent materials in our powerful cross reference tables.

Click on the property data link of interest to you to view specific property data.